1. Field of the Invention
The invention relates generally to sterilization methods and more particularly, to a method for sterilizing items using a multi-component vapor phase sterilant where one component is water.
2. Description of the Invention Background
Decontaminating instruments, such as air powered surgical or dental tools, or endoscopes having long, narrow lumens and other crevices, has always been a challenge. A variety of methods have been used to decontaminate these instruments. Examples include ethylene oxide, steam, formaldehyde and steam mixtures, dry heat, or liquid soaking. Instruments of this type, however, are very susceptible of damage from the high heat and/or moisture present in conventional decontamination systems.
In dentists' offices, where instruments must be used several times per day on different patients, it is important not only to sterilize the instruments between patients to prevent cross-contamination, but to do so quickly and economically without damaging the instrument.
A particularly troubling problem encountered in sterilizing instruments with long lumens or surface crevices is ensuring delivery of, and effective contact of, the sterilant with these hard to reach areas. Air pockets can form which create a shield of air against sterilant penetration.
It is known in steam sterilization systems to precondition the chamber to remove air. Preconditioning includes evacuation and pressurization of the chamber. U.S. Pat. Nos. 4,164,538; 4,335,071; and 4,687,635 are representative. Due to the damage that can be caused by the intense heat and moisture in steam sterilization, those methods are not suitable for sterilizing many instruments.
Several hydrogen peroxide vapor sterilization systems have been described in which the sterilant vapor is injected into an evacuated chamber. In one embodiment of a method disclosed in U.S. Pat. No. 4,956,145, a chamber is evacuated prior to the introduction of the hydrogen peroxide vapor to the closed chamber. Thereafter, intermittent make-up injections are made in variable amounts to maintain the concentration of the sterilant vapor in the chamber at a level below the saturation limit immediately following each such injection. The chamber is sealed throughout the cycle. One reason for the variable amounts of the make-up injections is the increase in relative humidity as the process proceeds.
In U.S. Pat. No. 4,909,999, a method is disclosed wherein hydrogen peroxide vapor is drawn into and through a chamber in a continuous flow-through sterilization cycle in which air is used as a carrier. The ambient air is drawn from the chamber prior to the introduction of the sterilant vapor-laden air flow.
None of these references focuses on the problems inherent in sterilizing instruments having long narrow lumens. There is a need for a sterilization method which will ensure contact between the sterilant and the hard to reach lumens and crevices of medical, surgical and dental tools. There is a further need for an economical low temperature sterilization method that will not damage the tools, that is not labor intensive and is not time consuming.
Finally, there is a need for a sterilization method that can be operated in an office setting without the risk of exposing personnel to hazardous chemical sterilants residues.